Add Alternatives section to archive module README (Fixes #705)

modules/archive/README.md

@@ -35,6 +35,12 @@ Additionally, if `pigz` and/or `pbzip2` are installed, `archive` will use them o
 their traditional counterparts, `gzip` and `bzip2` respectively, to take full advantage
 of all available CPU cores for compression.
 
+Alternatives
+------------
+
+Specifically on macOS, [The Unarchiver][1] provides a similar command line tool
+which doesn't depend on a number of other programs being installed.
+
 Authors
 -------
 
@@ -43,4 +49,4 @@ Authors
   - [Sorin Ionescu](https://github.com/sorin-ionescu)
   - [Matt Hamilton](https://github.com/Eriner)
 
-[1]: https://github.com/sorin-ionescu/prezto/issues
+[1]: https://theunarchiver.com/command-line